Process for interconnection of electronic power modules of a rotary electrical machine, and assembly of interconnected power modules obtained by means of this process

ABSTRACT

A method for interconnecting electronic power modules of a polyphase rotary electric machine. The power modules are disposed in open cavities of a heat sink and comprise substrates on which are provided MOSFETs of a synchronous rectifier bridge and integrated control circuits. The method comprises the production of: a planar connector ( 6 ) including at least one layer of conductive traces ( 64 ); a plurality of interconnection elements ( 512 ) arranged in multiple geometric formations and ultrasonically welded or brazed (S 2 ) directly to the substrates ( 51 ) and/or the MOSFETs; and openings ( 65 ) in the planar connector ( 6 ) allowing the free passage of the upper ends ( 5120 ) of the connection elements ( 512 ) and a mechanical contact with the conductive traces ( 64 ). The electrical connections are obtained by means of laser ( 8 ) transmission welding (S 1 ) or electric resistance welding.

CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM TO PRIORITY

This application is a national stage application of InternationalApplication No. PCT/FR2011/052673 filed Nov. 17, 2011, which claimspriority to French Patent Application No. 10/59632 filed Nov. 23, 2010,of which the disclosures are incorporated herein by reference and towhich priority is claimed.

The present invention relates in general to the field of rotaryelectrical machines, in particular for motor vehicles.

More particularly, it applies to alternators with synchronousrectification equipped with electronic power modules, and even moreparticularly to polyphase alternators.

For the sake of clarity of the concepts, reference will be madehereinafter to the preferred application of the invention, and it willbe assumed that the alternator is of the three-phase type, without thislimiting in any way the scope of the invention.

By way of example the French patent FR2886477B1 entitled“Interconnection part for a signal for a rotary electrical machine”describes a rotary electrical machine of the alternator-starter type,comprising electronic power means. These electronic power means are inthe form of modules of the so-called mechatronic type, including a powertransistor bridge which uses MOSFET technology, and ensure a reversiblefunction of an analogue-direct power converter (“AC/DC” according to theterminology commonly used).

In the mode of functioning as an alternator of the rotary electricalmachine, the aforementioned converter ensures the rectification of thealternating phase voltages produced by the alternator into a singledirect supply voltage (typically of 14 Volts) which supplies an on-boardsupply network of the motor vehicle. Conversely, as is well known topersons skilled in the art, in the mode of functioning as amotor/starter of the rotary electrical machine, the converter providesphase voltages which supply stator windings of the rotary electricalmachine. This therefore gives rise to rotation of the rotor of therotary electrical machine which has sufficient mechanical torque, suchas to ensure the starting of the thermal engine of the vehicle. Thephase voltages are obtained by cutting off, by means of the powertransistor bridge, the direct voltage of the on-board supply network(direct voltage supplied by an energy storage battery).

The electronic power means described in the aforementioned French patentFR2886477B1 comprise three identical modules, one per branch of thebridge, and a control module which incorporates a specialised integratedcircuit known by the acronym “ASIC” (for “Application—SpecificIntegrated Circuit” according to the terminology commonly used). Thebranch modules of the bridge each form a branch of the transistorbridge.

The architecture of the branch module of the bridge according to thispatent is described for example with reference to FIGS. 4A to 4E of theaforementioned French patent FR2886477B1. MOSFET transistors in the formof bare electronic chips are soldered onto connection gates known as“leadframes” in the terminology commonly used, which are over-moulded ina mechatronic case. These leadframes are kept placed on a metal baseplate by means of an electrically insulating small plate which issandwiched between the leadframes and the base plate. The small platehas properties of good thermal conduction, such as to transmit thecalories generated by the electronic chips to a heat sink which isplaced below the metal base plate of the module.

The technology which is disclosed by French patent FR2886477B1 hasvarious applications in rotary electrical machines, and in particulargives very good results in terms of quality and performance inapplications of the alternator-starter type which require a reversiblerectifier bridge.

However, as previously stated, it is necessary to place the electronicchips in a so-called mechatronic technology case.

These arrangements increase the complexity, in particular that of theinterconnection structure which is the main subject of this patent, aswell as the number of mechanical parts used, and consequently inparticular they increase the cost price.

Whilst maintaining the advantages of the devices according to the knownart, in particular those described in French patent FR-2886477B1, theobject of the invention is to eliminate the disadvantages of the latter,some of which have just been described.

Whilst proposing an architecture of interconnected electronic powermodules for an optimised polyphase rotary electrical machine, thesubject of the invention is a process for production of a structure forinterconnection of these power modules to one another on the one hand,and also of these power modules to other electrical components of thesaid rotary electrical machine.

For this purpose, according to an important characteristic of the saidarchitecture, the power modules are implemented directly in a heat sink,which in particular eliminates the need to encapsulate them in a case ofthe so-called mechatronic type, and this will make it possible tosimplify the elements of the inter-module interconnection structure.

According to a particular embodiment, the power modules each comprisethe electronic power circuits of two branches of a synchronous rectifierbridge, and control circuits of the electronic power circuits.

Preferably, the power circuits are produced on the basis of a MOSFETtransistor. The control circuits are preferably produced using so-called“ASIC” technology (acronym for the expression commonly used“Application-Specific Integrated Circuits”). The power modules comprisethe actual electronic power circuits and the control circuits present inthe form of substrates using so-called “DBC” technology (acronym for theexpression commonly used “Direct Bonded Copper”) which has manyadvantages, in particular good thermal conductivity. The substrate isconstituted by three layers comprising a lower layer made of copper, amedian insulating layer made of ceramic (alumina, beryllium oxide,etc.), and an upper layer made of conductive material, generally copper.This layer is subdivided into a plurality of conductive tracks, theelectronic components of the power module being soldered on thesetracks. This technology is well known to persons skilled in the art, anddoes not need to be described in greater detail hereinafter.

According to another characteristic of the architecture of power modelsimplemented in the present invention, the heat sink comprises cavitiesopen in one of its surfaces which are each designed to receive one ofthe said power modules. The power modules are bonded directly on thebase of the cavities in the sink. Preferably, after assembly, thesecavities are filled with gels such as to cover and insulate the powermodules.

According to an important characteristic of the process forimplementation of the interconnection structure according to theinvention, the interconnections between the terminals of the phasewindings of the rotary machine, the terminals of the source of directelectrical energy of the vehicle (generally a positive terminal known asB+ and B− or ground) and the power terminals of the branches of therectifier bridge and for the signal of the control circuits, areproduced firstly by means of first interconnection means comprising aplate made of insulating material, for example plastic, comprising aplurality of conductive tracks, which for example are made of copper,and, secondly, a plurality of input-output elements for connection withthe electronic circuits of the aforementioned substrates. The firstinterconnection means will be known hereinafter as flat connectors, forthe purpose of simplification of the description.

According to yet another important characteristic of the processaccording to the invention, the said connection elements are producedsimply on the basis of filamentary components made of conductivematerial, of the type such as tongues, nails, studs or pins, and canhave various mechanical and geometric configurations which will bedescribed hereinafter.

According to yet another important characteristic of the processaccording to the invention, the said connection elements are soldered orwelded by ultrasound directly onto the substrates and/or onto theelectronic power components of the said power modules, such as to becontained on planes at right angles to the aforementioned substrateplanes which are arranged in the cavities in the heat sink.

According to yet another important characteristic of the processaccording to the invention, the electrical connections between firstlythe input-output elements for connection of the electronic circuits, andsecondly conductive tracks of the flat connector, are obtained by a stepof welding of the electrical type by resistance, or of the laser type bytransparency. According to yet another characteristic of the processaccording to the invention, the first subassembly constituted by thepower modules and the heat sink and the flat connector are securedmechanically to one another after carrying out the steps of electricalconnections by soldering or welding by ultrasound of the connectionelements, firstly onto the substrates and/or the power components, andsecondly onto conductive tracks of the flat connector.

The main object of the invention is thus a process for interconnectionof at least two electronic power modules of a polyphase rotaryelectrical machine to one another, and of the said power modules tospecific components of the said polyphase rotary electrical machine, thesaid power modules comprising a substrate comprising a layer constitutedby a first plurality of conductive tracks on which there are implementedsemiconductor power components and integrated electronic controlcircuits of these components which are connected electrically by thesaid conductive tracks, characterised in that it comprises an initialphase comprising a step consisting of arranging the said substrates inopen cavities on a so-called upper surface of a support unit, such as tobe incorporated in a first plane of the space, a subsequent phase ofproduction of the said interconnections comprising at least thefollowing steps:

-   -   a step of production of first interconnection means constituting        a flat connector comprising at least one layer constituted by a        second plurality of conductive tracks which is supported by at        least one plate, known as the lower plate, made of insulating        material, such as to form a network of electrical connections        with a predetermined configuration;    -   a step of production of a plurality of connection elements in        each of the said power modules, constituted by filamentary        components made of conductive material, with specific geometric        forms, and of their electrical connections, by soldering or        welding by ultrasound, at a first so-called lower end, on the        said conductive tracks of the said substrates and/or on the said        electronic power components, such that they are incorporated on        planes substantially at right angles to the said first plane of        the space;    -   a step of production of recesses in at least one said lower        plate of the said flat connector, the spatial distribution of        the said recesses corresponding to the spatial distribution of        the said connection elements;    -   a step of placing the said flat connector above the said        connection elements, on a plane parallel to the said first plane        of the space, such that the second, so-called upper ends of the        said connection elements can be put into contact with the said        conductive tracks of the said connector through the said        openings; and    -   the production of electrical connections between the said upper        ends of the said connection elements and the said conductive        tracks, by welding.

The object of the invention is also an assembly of interconnected powermodules obtained by means of this process.

The invention will now be described in greater detail with reference tothe attached drawings, in which:

FIG. 1 illustrates schematically, in longitudinal cross-section, anexample of a structure of a rotary electrical machine according to theknown art;

FIG. 2 illustrates schematically an example of a voltage rectifiercircuit of the type with synchronous rectification;

FIG. 3 illustrates in space and in exploded view the main subassembliesof an example of a preferred architecture of power modules and theirinterconnections for implementation of the process of interconnection ofpower modules according to the invention;

FIG. 4 illustrates schematically the mounting of the power modules inthe cavities in the sink represented in FIG. 3;

FIG. 4A is a detailed view of a connection element represented in FIG.4;

FIG. 5 is a partial view of the sink and of a power module representedin FIG. 4, illustrating another embodiment of the connection elements;and

FIGS. 6A to 6D illustrate four embodiments according to the invention ofelements for connection of the power modules to an interconnectionconnector, and the welding processes implemented in these embodiments.

Hereinafter, without in any way limiting the scope of the invention, thecontext will be the preferred application of it, unless otherwisestated, i.e. the case of an alternator with synchronous rectification ofthe double three-phase type, comprising three power modules, eachcomprising the electronic power circuits of two branches of a rectifierbridge and control circuits for these electronic power circuits.

Also hereinafter, elements which are identical or at least similar inthe figures bear the same references, and will be described again onlyif necessary.

Before describing the invention, it is advantageous to recall brieflythe general structure of a machine of this type and an example ofelectronic power circuits of the rectifier bridge and of an electroniccircuit for control of these circuits, with reference to FIGS. 1 and 2.

FIG. 1 illustrates highly schematically, in longitudinal cross-section,an example of a structure of a rotary electrical machine Mt according tothe known art, i.e. in this case a three-phase alternator withsynchronous rectification. This alternator comprises in a conventionalmanner a stator S and a rotor R, as well as an electronic power module,which contains the actual electronic power circuits (rectifier bridge)and control circuits for these power circuits.

FIG. 2 illustrates an example of a configuration of electrical andelectronic circuits which can be implemented in the three-phasealternator Mt in FIG. 1.

As illustrated in FIG. 2, the alternator-starter Mt is associated withelectronic power and control circuits with the general reference 1.These circuits comprise a synchronous voltage rectifier bridge 2 and avoltage regulator 3. The rotor R is rotated by a drive shaft whichconnects it to the crankshaft of the thermal engine 5 of the vehicle(not illustrated in FIG. 1)

In this embodiment, the alternator Mt is a three-phase machine of theLundell type.

FIG. 2 illustrates schematically an example of a voltage rectifiercircuit 2 of the type with synchronous rectification. This comprisessubstantially a voltage rectifier bridge constituted by three branchesB₁ to B₃ and control circuits 3 of the bridge 2.

In the example described, each branch B₁ to B₃ of the bridge 2 comprisestwo power transistors in cascade of the MOSFET type, T_(1H)-T_(1B),T_(2H)-T_(2B), T_(3H)-T_(3B) respectively. The signs H and B signifyarbitrarily the top and bottom of the branch respectively. The top endsof the branches B₁ to B₃ are connected to the terminal B+ and the bottomends are connected to the terminal B− (generally connected to theground) of a direct electrical energy storage unit (battery of thevehicle, not illustrated in FIG. 2). In a conventional manner,anti-parallel diodes D_(1H) to D_(3B) are connected to the source anddrain terminals of the MOSFET transistors T_(1H) to T_(3B).

The branches B₁ to B₃ are connected at their middle points to the threephase outputs φ₁ to φ₃ of the stator windings S.

The control circuits 3 supply to the gates of the MOSFET transistorsT_(1H) to T_(3B) control signals CG_(1H) to CG_(3B) respectively.

The control circuits 2 comprise circuits for forming the gate controlsignals (not explicitly illustrated in FIG. 2), which carry out formingadapted to the signals CG_(1H) to CG_(3B) such as to obtain functioningwith synchronous rectification of the MOSFET transistors T_(1H) toT_(1B) of the bridge 2. This type of functioning with synchronousrectification of the MOSFET transistors T_(1H) to T_(1B) is well knownto persons skilled in the art, and need not be described in greaterdetail hereinafter.

The control circuits 2 also comprise regulation circuits (not explicitlyillustrated in FIG. 2), such as to supply a direct voltage withpredetermined precision between the terminals B+ and B−, conventionallyof +12 V. This type of circuit is also well known to persons skilled inthe art, and need not be described in greater detail hereinafter.

Also, these control circuits 3 supply an excitation current of thewinding of the stator S.

Finally, the control circuits 3 can comprise circuits for detection oferrors and/or of malfunctioning of the rectifier bridge 2, in particularin order to protect the MOSFET transistors T_(1H)-T_(1B) if an overloadis detected.

In the known art, and in particular that described by patentFR2886477B1, the bridge 2 is in reality divided into three partscorresponding to the three bridge branches B₁ to B₃. Each branch B₁ toB₃ is in the form of a substrate encapsulated in an independentso-called mechatronic case, and the control circuits are produced in theform of an “ASIC” integrated circuit, the assembly being completed byelectrical interconnection and mechanical securing means. As stated inthe preamble of the invention, this architecture has a certain number ofdisadvantages which need not be described here.

In the present invention, whilst retaining the general structure of arotary machine according to the known art and the configuration of theelectronic circuits as such, which represents a certain advantage, anarchitecture of optimised interconnected modules is adopted which nolonger requires the modules to be packed in cases, and permitssimplification of the connection means. For this purpose, partitioningand physical implementation of the circuits are provided which avoid theaforementioned disadvantages, and make it possible to achieve theobjectives set out, as will now be shown in relation with FIGS. 3 to 6D.

FIG. 3 illustrates in space and in exploded view around an axis oflongitudinal symmetry A, the main subassemblies of an example ofpreferred architecture of power modules in which the process forinterconnection according to the invention will be implemented.

The architecture illustrated in this figure relates to an alternator ofthe double three-phase type, and comprises three subassemblies which arespecific to the invention, i.e. a heat sink 4, a series of power modules5, with references 51 to 53, and means 6 for electrical interconnectionbetween the series of modules 5. The power modules 5 of the series eachcomprise the electronic circuits of two rectifier bridge branches andthe corresponding control circuits.

According to an important characteristic of the invention, the heat sink4 is provided on its upper surface (in FIG. 3), which is substantiallyflat, with three open cavities 41 to 43 with a flat base which aredesigned to receive the modules 51 to 53. The lower surface of the sink4 is provided in a conventional manner with fins 45 or similar unitswhich are designed to improve the heat exchanges with the ambient air.

The heat sink 4 is in the general form of a “horseshoe” (arc of acircle) such as to allow free passage of the air in its central part,for the purpose of cooling of the inner units of the rotary machine(windings, etc.), of which only the upper mechanical part 7 (rearbearing) is represented in FIG. 3. In a habitual manner, the ambient airis aspirated towards the interior of the rotary machine by a fan whichrotates with the rotor (not represented in FIG. 3). The part 7 comprisesa plurality of orifices (with no reference) surrounding a centralorifice 70 which is designed to receive a bearing capsule, and lateralorifices 71 which allow the air to enter the interior of the rotarymachine.

In a conventional manner, after final assembly, the three sub-assemblies4 to 6 are secured mechanically to the mechanical part 7 by anyappropriate means (screws, etc.), with the “horseshoe” covering theperiphery partially.

Each module 51 to 53 comprises a substrate which contains the electronicpower circuits themselves (the MOSFET transistors of two branches of thehexaphase rectifier bridge) and control circuits of this bridge.

According to another characteristic of this architecture, the controlcircuits are distributed in the three modules 51 to 53, and are notcentralised as for the example of the three-phase alternator in FIG. 2.They are in the form of integrated circuits which are preferablyproduced using “ASIC” technology.

Apart from these specific features, the functional diagrams of the powerand control circuits implemented in the known art can be retained withinthe context of the invention, which represents an additional advantageas already indicated, since a new functional design of these circuits isnot necessary.

The power and control circuits are arranged on a substrate, allpreferably produced using “DBC” technology, and constituting theaforementioned power modules 51 to 53. The substrates of the modules 51to 53 will be described hereinafter with reference to FIG. 4. Connectionelements (FIG. 3: under the general references 512, 522 and 532) whichcan have various configurations (and will be described in detail withreference to FIGS. 6A to 6D) are soldered or welded by ultrasounddirectly on the substrates of the modules 51 to 53, according to one ofthe important characteristics of the process for interconnection ofpower modules according to the invention. They make it possible toestablish electrical connections with the means 6 for interconnectionbetween modules 5. After the soldering or welding by ultrasound, theconnection elements are incorporated on a plane which is substantiallyat right angles to the substrates.

The means 6 for interconnection are in the general form of a plate whichconstitutes a flat electrical connector. This plate comprises one or aplurality of flat layers made of insulating material, for exampleplastic of the PPS type. This plate supports a plurality of conductivetrails or tracks, which for example are made of copper or any otherappropriate metal, and can convey firstly so-called “strong” electriccurrents (connections with the terminals B+ and B− of the battery, theterminals of the branches of the rectifier bridge which are distributedin the modules 51 to 53, and the terminals of the windings of the rotarymachine), and secondly so-called “weak” currents (control signals). Theconductive tracks can be over-moulded and sandwiched between layers ofinsulating material of the plate 6.

Each aforementioned connection element, welded on the substrates of themodules 51 to 53, is connected electrically to one or a plurality ofconductive tracks, such as to form a network of interconnections with apredetermined configuration which connects the modules 51 to 53 to oneanother and a voltage regulator, which is also present in the alternatoron the one hand, and these modules 51 to 53 on the other hand, to therectified output voltage and phase terminals (terminal B+ and ground) ofthe alternator. For this purpose, the plate 6 which forms a connectorhas a geometry similar to that of the heat sink 4 (form of a“horseshoe”), such that the plate can be secured mechanically on thesink, after assembly of the modules 51 to 53, in the cavities 41 to 43.

The plate 6 additionally comprises areas under the general reference 60which leave free access to the conductive tracks, the dimensions andspatial distribution of which are adapted to those of the connectionelements 512, 522 and 532 which are soldered on the substrates of themodules 51 to 53.

The mechanical connection of the two subassemblies, i.e. the heat sink 4and connector 6, is carried out by any conventional means well known topersons skilled in the art (screwing, etc.). For the sake of clarity ofthe concepts, FIG. 3 represents schematically means for securing withthe general references 44 (heat sink 4) and 61 (connector 6). Inaddition, as already indicated, this assembly is also securedmechanically on the part 7 by any conventional means (not represented inFIG. 3).

FIG. 4 illustrates schematically, seen from above in space, the mountingof the modules 51 to 53 in the cavities 41 to 43 of the sink 4.

The modules 51 to 53 comprise substrates, only the upper layers of whichhave references, 510 to 530. These substrates are preferably producedusing “DBC” technology. FIG. 4 also represents integrated circuits 511to 531 which are supported by the substrates. In this embodiment of theinvention, a single control circuit 511, 521 or 531 is provided permodule 51 to 530. However, it should be understood that these modulescan comprise a plurality of integrated circuits: in particular thebridge control circuits, which are preferably produced using “ASIC”technology, and the MOSFET transistors. Finally, connection elements arerepresented schematically. These connection elements are soldereddirectly on conductive tracks and/or on the integrated circuits of themodules 51 to 53, and are designed to establish galvanic contacts withthe conductive tracks of the connector 6 (FIG. 3).

The geometric configurations and the embodiments of these elements,which constitute one of the important characteristics of the invention,will be described hereinafter with reference to FIGS. 6A to 6D.

A single connection element has specifically been given a reference inFIG. 4, i.e. the connection element 512 of the module 51, which isillustrated in greater detail in FIG. 4A.

The element 512 has the general form of a tongue made of conductivematerial bent back into a “Z”, with a flat lower surface which is inelectrical contact with the substrate of the modules 51 to 53, and aflat upper surface which is designed to be put into electrical contactwith one of the tracks of the connector 6 (FIG. 3). This embodimentcorresponds to that which will be described with reference to FIG. 6A.

FIG. 5 illustrates another embodiment of connection elements, in theform of vertical cylindrical studs, of the semiconductor diode end type,or similar components (resistor, etc.).

In FIG. 5, only the central part of the heat sink 4 is shown, i.e. thepart corresponding to the cavity 42 and the module 52. With theexception of the embodiment of the connection element 522′, the otherelements in FIG. 5 are identical to those in FIG. 4, and need not bedescribed again. This embodiment of the connection element correspondsto that which will be explained more particularly with reference to FIG.6B, but it can also be implemented for the elements corresponding tothose which will be explained with reference to FIGS. 6C and 6D.

Irrespective of the embodiment of the connection elements selected, themodules 51 to 53 are secured in the cavities 41 to 43 by bonding on thebase of these cavities, directly on the sink 4, i.e. withoutintermediate elements, contrary to the known art described by Frenchpatent FR2886477B1. For the sake of clarity of the concepts, a glue ofthe silicon thermal type can be used for this purpose. After assembly ofthe modules 51 to 53 in the cavities 41 to 43, the latter can be filledwith a gel such as, for example, a two-component silicone gel, whichmakes it possible to insulate the semiconductor components electrically,and to provide mechanical protection.

For the sake of clarity of the concepts, and without this limiting inany way the scope of the invention, a description will now be provided,with reference to FIGS. 6A to 6D, of four main embodiments of connectionelements, as well as of the corresponding processes for connection ofthese connection elements to the conductive tracks of the connector 6(FIG. 3).

FIG. 6A illustrates schematically a connection element 512 constitutedby a flat tongue made of conductive material, which is bent in themanner of an accordion in order to assume the general form of a “Z”.This embodiment corresponds to that which is illustrated in FIG. 4.

FIG. 6A represents schematically the substrate of the module 51, and itis assumed that it comprises a plate of insulating material 511,sandwiched between an underlying plate of conductive material 513 andconductive tracks 510 which run on the upper surface. The configurationis identical for the other substrates 52 or 53.

Each connection element 512 is welded (by means of the lower branch 5121of the “Z”) on a conductive track 510, or alternatively on asemiconductor element (MOSFET of the rectifier bridge not represented inFIG. 6A) by welding S₂. The upper layer 510 is constituted by aplurality of tracks for interconnection between the input and/or outputterminals of the components of the power module (51 in the example inFIG. 6A) welded onto this layer.

FIG. 6A also represents a portion of the connector 6 overhanging themodule 51 and the connection element 512. It is assumed in the exampledescribed that the connector 6 comprises a single layer 64 of tracks ofconductive material, sandwiched between two plates of insulatingmaterial, i.e. an upper 62 and a lower 63 plate. It will be appreciatedthat it must be understood that the invention is not limited to a singlelayer of conductive tracks. In fact, according to a variant embodimentnot represented, it is possible to provide a plurality of superimposedlayers of conductive tracks which are separated by plates of insulatingmaterial.

Recesses 65 are provided in the areas of the insulating plates 62 and 63which overhang the upper branches 5120 of the connection elements 512.

According to this embodiment, as a result of their form in the shape ofa “Z” and the resilient properties of the material which constitutes thetongue, the connection elements 512 are provided with a “spring”function, which makes it possible to ensure good mechanical contact byexerting a support force when the connector 6 is put into place.

The tracks 64 of the connector 6 are welded on the connection element512 (on the upper branch 5120 of the “Z”) by laser welding bytransparency, i.e. through the conductive track 64 by welding S₁. Thelaser 8 which makes possible this operation is illustrated schematicallyin FIG. 6A, as is the beam emitted f1 which converges on the upperbranch 5120 of the “Z”.

A laser weld has the advantage of requiring less energy than welding byresistance. There is therefore less risk of damaging the soldering onthe substrates and the semiconductor components (MOSFETS).

For the sake of clarity of the concepts, the characteristics of theprocess for production of the electrical connections are typically asfollows:

-   -   ideally, the thickness of the track 63 to be passed through        should not exceed 0.6 mm;    -   the thickness of the track situated below (i.e. the upper branch        5120 of the “Z”) must be at least equal to the thickness of the        track passed through 64;    -   the maximum play admissible between the tracks 64 and 5120 for a        through weld is approximately 20% of the thickness passed        through, i.e. 0.12 mm in the example selected;    -   a pressure force on the connector 6 is necessary and must be        calculated so as not to damage the substrate 52 and its        components;    -   in order to obtain a good laser weld by transparency, the track        above 64 must be subjected to a mat surface treatment of the        nickel plating type in order to limit the reflection of the        laser beam (for example by using the nickel plating technology        known as “Sulfamat”—registered trademark). On the other hand,        tin and phosphorus are not acceptable because they are liable to        create cracks in the weld.

FIG. 6B illustrates schematically a connection element 522′ constitutedby a cylindrical stud made of conductive material, perpendicular to theplane of the upper layer 520 of the substrate 52 (or of the othersubstrates 51 or 53). The stud 522′ comprises a base 5220′ with a largerdiameter soldered directly (by welding S₂) on the upper layer 520 of theunderlying substrate 52 (or alternatively on a power component i.e.MOSFET, not represented). The upper layer 520 is constituted by aplurality of tracks for interconnections between the input and/or outputterminals of the components of the power module (52 in the example inFIG. 6B) welded on this layer. This embodiment corresponds to that whichis illustrated in FIG. 5.

According to this embodiment, and in the example described in FIG. 6B,the connector, which henceforth has the reference 6′, is assumed tocomprise, as in the example in FIG. 6A, a single layer of conductivetracks 64′, sandwiched between two plates of insulating material 62′ and63′. On the other hand, again in this embodiment, it is necessary forthe conductive track 64′, and not only the insulating plates 62′ and63′, also to be provided with a receptacle 65′ in order to allow freepassage at the upper end of the connection element 522′ through thestack of layers 62′-64′-63′. One of the ends 640′ of the conductivetrack 64′ is extended into the recess area 65′. It is bent back by 90°upwards. The latter comprises a dish 6400′ which is designed to be putinto contact with the connection element 522′ in its upper part.

In this embodiment, the weld between the track 64′ and the connectionelement is produced by a process of welding by resistance at the levelof the dish 6400′. This is a process well known to persons skilled inthe art. It is commonly used, in particular in order to weld ends ofsemiconductor diodes or equivalent components.

For the sake of clarity of the concepts, according to this variant, thecharacteristics of the process for production of the electricalconnections is typically as follows:

-   -   the process of welding by resistance is well controlled, and        does not pose a particular problem if the elements to be welded        (studs 522′ and track 64′) have dimensions similar to those of        the aforementioned semiconductor diodes;    -   typically, the studs 522′ have a diameter of 1.2 mm;    -   as a variant, instead of being cylindrical, the studs 522′ can        be provided with a square or rectangular cross-section, if the        bent-back tongue 640′ of the track 64′ comprises a dished pin;    -   typical parameters of the welding are as follows: force of 35        DaN, electric current of approximately 8000 A with 2 V for a        period of time of 20 to 30 ms. The electrodes must descend to a        minimum of 1.5 mm below the boss 6400′ of the track 64′.

FIG. 6C illustrates an additional variant embodiment of the connectionelements, which henceforth have the reference 512″.

As previously, the connection element 512″ is constituted by acylindrical stud made of conductive material, perpendicular to the planeof the upper layer 510 of the substrate 51 (or of the other substrates52 or 53). The base 5121″ of the latter, which can be constituted bybending back at 90°, is soldered (weld S₂) on the upper layer 510 of theunderlying substrate 51 (or alternatively on a power component: MOSFET,not represented in FIG. 6C). It is assumed, as previously, that there isa single conductive track 64″ sandwiched between two plates made ofinsulating material 62″ and 63″. Also as previously, this conductivetrack 64″ is pierced by an orifice 65″, and is extended into the recessarea whilst allowing the end of the stud 512″ to pass through. The upperpart 5120″ of the element of the stud 512″ is bent back by 90°, such asto come into contact with the upper surface of the end of the conductivetrack 64″.

As for the connection embodiment described with reference to FIG. 6A,the weld is of the laser weld by transparency type, and has theadvantages previously described. It is therefore the bent-back part5120″ of the pin which the laser beam passes through (not explicitlyrepresented in FIG. 6C) and which is welded on the conductive track 64″by welding S₁.

For the sake of clarity of the concepts, the characteristics of theprocess for production of the electrical connections are typically asfollows:

-   -   the track which the laser beam must pass through, i.e. the        bent-back part 5120″ of the stud 512″, can be finer, with a        thickness which can be as little as 0.3 mm, which makes        possible;    -   a lower level of energy necessary for welding;    -   a conductive track thickness 64″ of 0 8 mm to 1 mm, in order for        the current to pass through;    -   no need to resort to nickel plating of the tracks 64″ of the        connector 6″;    -   the contact between the tracks 64″ and studs 512″ is ensured        simply by the bending operation.

FIGS. 6D illustrates an additional variant embodiment of the connectionelement, henceforth with the reference 512′″. The latter is similar tothe connection element 512″ as far as its spatial configuration isconcerned, but it has a rectangular or square cross-section, and is notbent in its upper part. Its base 5121′″, which can be bent back to ahorizontal position, is soldered (weld S₂) on the upper layer 510 of theunderlying substrate 51 (or alternatively on a power component: MOSFET,not represented).

As previously, it is assumed that the connector 6′″ comprises only asingle layer of conductive tracks 64′″, sandwiched between twoinsulating plates 62′″ and 63′″. It is also firstly necessary to providea total opening 65′″ in the insulating plates 62′″ and 63′″, and in theconductive track 64′″, such as to allow the upper end of the stud 512′″to pass through, and secondly a track end 640′″ which is bent back by90° upwards, and is put into contact with the upper end of the stud ′″.

The welding is also carried out according to the laser process bytransparency, using a laser similar to that represented in FIG. 6A. Therelative arrangement of the two elements makes it possible to carry outlaser welding (weld S₁) with raised edges on the respective ends of theconductive track 64′″ and of the stud 512′″.

For the sake of clarity of the concepts, the characteristics of theprocess for production of the electrical connections according to thisvariant are typically as follows:

-   -   this solution requires tooling in order to place the conductive        track 64′″ against the stud 512′″, since the maximum play in        order to weld these elements correctly must not exceed 5% of the        thicknesses of the elements in contact;    -   the laser must be equipped with a vision adjustment system, or        it must be mounted on the aforementioned placing tool, in order        to ensure correct welding at the junction of the conductive        track 64′″ and the stud 512′″;    -   nickel plating is possible on one or the other of the surfaces        of the elements to be welded, or on both, but is no longer        necessary;    -   for a track 64′″ of the connector 6 with a thickness of 0.8 mm,        the soldered connection element 5121′″ must have a minimum        thickness of 0.4 mm, and its thickness should preferably be        identical to that of the conductive track 64′″ at its end 640′″.

Reading the preceding description easily shows that the inventionachieves well the objectives set out by it, and which need not berecalled in full.

However, the process for interconnection of power modules according tothe invention is not limited simply to the embodiments explicitlydescribed with reference to FIGS. 3 to 6D. Similarly, the assembly ofelectronic power modules obtained by means of the interconnectionprocess according to the invention does not apply only to an alternatorwith a bridge with synchronous rectification, which constitutes thepreferred application of it, but more generally to any polyphase rotaryelectrical machine comprising at least two power modules to beinterconnected via connection elements, one of the ends of which issoldered or welded by ultrasound on these modules, and the other end ofwhich is welded on a conductive track of a connector comprising at leastone layer of conductive tracks supported by at least one insulatingplate.

The invention claimed is:
 1. Process for interconnection of at least twoelectronic power modules of a polyphase rotary electrical machine to oneanother, and of said power modules to specific components of saidpolyphase rotary electrical machine, said power modules comprising asubstrate comprising a layer constituted by a first plurality ofconductive tracks on which there are implemented semiconductor powercomponents and integrated electronic control circuits of thesecomponents which are connected electrically by said conductive tracks,comprising a step consisting of arranging said substrates (51 to 53) inopen cavities (41 to 43) on an upper surface of a support unit (4), suchas to be incorporated in a first plane of the space, and a subsequentphase of production of said interconnections comprising at least thefollowing steps: a step of production of first interconnection meansconstituting a flat connector (6) comprising at least one layer (64)constituted by a second plurality of conductive tracks which issupported by at least one plate (63), known as the lower plate, made ofinsulating material, such as to form a network of electrical connectionswith a predetermined configuration; a step of production of a pluralityof connection elements (512) in each of said power modules (51 to 53),constituted by filamentary components made of conductive material, withspecific geometric forms, and of their electrical connections, bysoldering or welding by ultrasound, at a first lower end (5121), on saidconductive tracks of the substrates (51 to 53) and/or on said electronicpower components, such that they are incorporated on planessubstantially at right angles to said first plane of the space; a stepof production of recesses (65) in at least said lower plate (63) of saidflat connector (6), the spatial distribution of said recessescorresponding to the spatial distribution of said connection elements(512); a step of positioning said flat connector (6) above saidconnection elements (512), on a plane parallel to said first plane ofthe space, such that second, upper ends (5120) of said connectionelements (512) can be put into contact with said conductive tracks (64)of said connector (6) through said openings (65); and the production ofelectrical connections between said upper ends (5120) of said connectionelements (512) and said conductive tracks (64), by welding.
 2. Processaccording to claim 1, characterized in that the step of production ofsaid flat connector (6) comprises the assembly in a sandwich of at leastone layer of conductive tracks (64) between two plates made ofinsulating material (62, 63), said insulating tracks (64) comprisingconnections with strong power which convey currents for interconnectionbetween one another of said semiconductor power components and specificelectrical elements (φ1 to φ3, B+, B−) of said rotary machine (Mt) andconnections with low power which convey control signals forinterconnection of said integrated electronic control circuits (3). 3.Process according to claim 1, characterized in that it comprises, beforethe production of said electrical connections by soldering or welding byultrasound, a step consisting of bending said filamentary componentsmade of conductive material in an accordion, in order to provide themwith the general geometric form of a “Z”, and to give them a springeffect when they are subjected to a compression force, in that the lowerbranches (5121) of said “Zs” are soldered or welded by ultrasound (S2)on said conductive tracks (510) of the substrates (51) and/or saidelectric power components, in that the step of positioning of said flatconnector (6) above said connection elements (512) consists of exertinga support force on said flat connector (6), such as to obtain amechanical contact, via the lower surfaces of said conductive tracks(64) and through said orifices (65), with said upper branches of the“Zs” (5120), by means of said spring effect, and a step of electricalconnection of said conductive tracks (64) and said upper branches of the“Zs” (5120) by laser welding by transparency (S1) through the thicknessof said conductive tracks.
 4. Process according to claim 1,characterized in that said step of production of recesses consists ofproducing recesses (65″) which pass through each plate (62″, 63″) madeof insulating material of said connector (6″) and said layer ofconductive tracks (64″), the ends of said conductive tracks of beingextended into said areas of recess (65″), in that it comprises, beforethe production of said electrical connections by soldering or welding byultrasound (S2), a step consisting of bending by 90° the said lower ends(5121″) of these said filamentary components (512″), a step of solderingor welding by ultrasound (S2) of said lower ends (5121″) on saidconductive tracks (510) of the substrates (51) and/or on said electronicpower components, in that, during said step of positioning of said flatconnector (6″), said upper ends (5120″) of the connection elements(512″) are inserted in said orifices (65″) and bent back by 90° on theupper surfaces of said ends of conductive tracks (64″) of said flatconnector (6), such as to obtain a mechanical contact, and in that itcomprises a step of electrical connection of said conductive tracks(64″) and said upper ends (5120″) by laser welding by transparency (S1)through the thickness of said ends (5120″) of the connection elements(512″).
 5. Process according to claim 1, characterized in that said stepof production of recesses consists of producing recesses (65′″) whichpass through each plate (62′″, 63′″) made of insulating material of saidconnector (6′″) and said layer of conductive tracks (64′″), the ends ofsaid conductive tracks (640′″) being extended in said areas of recess(65′″), in that it comprises a step consisting of bending said ends ofconductive tracks (640′″) by 90° towards the upper surface of the saidflat connector (6′″), in that it comprises, before the production ofsaid electrical connections by soldering or welding by ultrasound (S2),said filamentary components being provided with a rectangularcross-section, a step consisting of bending by 90° said lower ends(5121′″) of said filamentary components (512′″), in that it comprises astep of soldering or welding by ultrasound (S2) said lower ends (5121′″)on said conductive tracks (510) of the substrates (51) and/or on saidelectronic power components, in that, during said step of positioning ofsaid flat connector (6′″), said upper ends of connection elements(512′″) are inserted in said orifices (65′″) and placed against saidends (640′″) of conductive tracks (64′″) bent by 90°, such as to obtaina mechanical contact, and in that it comprises a step of electricalconnection of the said ends (640′″) of conductive tracks (64′″) and ofsaid upper ends of connection elements (512′″) by raised-edge laserwelding (S1) of these ends.
 6. Process according to claim 1,characterized in that said step of production of recesses consists ofproducing recesses (65′) which pass through each plate (62′, 63′) madeof insulating material of said connector (6′) and said layer ofconductive tracks (64′), the ends of said conductive tracks (640′) beingextended into said areas of recess (65′), in that it comprises a stepconsisting of bending said ends of conductive tracks (640′) by 90°towards the upper surface of said flat connector (6′) and producingdishes (6400′) in them, in that it comprises a step of soldering orwelding by ultrasound (S2) on said conductive tracks (520) of thesubstrates (52) and/or on said electronic power components of said lowerends of said filamentary components (522′) at the level of a base(5220′) of said lower ends, in that, during said step of positioning ofsaid flat connector (6′), said upper ends of connection elements (522′)are inserted in said orifices (65′) and placed against said dishes(6400′), such as to obtain a mechanical contact, and in that itcomprises a step of electrical connection of said dishes (6400′) and ofsaid upper ends of connection elements (522′) by electric welding byresistance.
 7. Assembly of interconnected power modules of a polyphaserotary electrical machine, characterized in that it is obtained by theprocess according to claim
 1. 8. Assembly according to claim 7,characterized in that said power modules comprise substrates on whichthere are implemented electronic power components which constitute thebranches of a synchronous rectifier bridge and integrated electroniccontrol circuits for these branches of a synchronous rectifier bridge.9. Assembly according to claim 8, characterized in that said substratesare produced according to “DBC” technology, and consist of at least onelower layer (513) made of conductive material, of an intermediate layer(511) made of insulating material, and an upper layer (510) constitutedby a plurality of tracks made of conductive material, on which there aresoldered said semiconductor power components (T1H-T1B) and saidintegrated electronic control circuits (3), and in that said connectionelements (512 to 532) are soldered or welded by ultrasound on saidtracks of the upper layer (510) and/or on said semiconductor powercomponents.
 10. Assembly according to claim 8, characterized in thatsaid integrated electronic control circuits (3) are produced in the formof specialised integrated circuits according to “ASIC” technologyimplemented on said substrates.